(CNN) -- Parts of northeast Australia braced for more flooding Thursday, a day after the nation's prime minister promised aid to flood-ravaged towns, and half of the state of Queensland was declared a disaster zone.

Emerald, an inland city of 15,000 residents, had essentially been isolated by flood waters and was accessible only by helicopter.

"Things have changed drastically overnight," said Megan Lewis, a radio reporter with the Australian Broadcasting Corporation, in an interview from the city on Thursday. "Yesterday the town was expecting things to not be so bad."

Waters have reached 15.4 meters (51 feet) there and are expected to rise another meter on Friday, she said. Lewis did not specify exactly where in the town that level was reached.

Some Emerald residents have been making their way to evacuation centers around the city, while others are stockpiling food and supplies.

On Wednesday, the Australian government provided two Blackhawk helicopters to help evacuate all 300 residents from the town of Theodore, one of the worst affected by the floods.

Queensland Emergency Services Minister Neil Roberts said Theodore was one of about 20 communities that had to be evacuated because of the floods.

"Most of our major river systems have been in flood over the last week," Roberts told CNN.

Besides Emerald, the other major population center threatened by flooding is Rockhampton, a city of 50,000 on the coast, he said.

Forecasters have said the weather would clear over the next 48 hours, Roberts said, but the heavy rain the area has had so far means water has built up in river catchment areas.

"It does take a day to three days, in some instances, for that water to come down in some of the cities that are under threat, so we're over the worst of the rain, but some of the worst flooding is still yet to come," he said.

The Bureau of Meteorology said flood warnings remained in place for many areas of Australia, with major and moderate flooding still occurring throughout much of Queensland's southern half.

Acting Attorney General Brendan O'Connor said the government would continue to monitor the situation in disaster-declared areas across Australia and work with state authorities to provide more assistance.